The present invention relates to a device capable of freely converting the rate of die-working speed relative to upper punch speed during powder mold pressing.
Generally, when pressing powder through a withdrawal-type press, the timing and speed of descent of a die relative to an upper punch is controlled as in, for example, Japanese Patent Publication No. S62(1987)-29160.
Said example is, as depicted in FIG. 2, a floating die press comprising an upper ram 101, lower press plate 116, a hydraulic cylinder 118 mounted on said ram 101, the lower end of a piston thereof being abuttable to a rack 122, as well as an oscillating lever 123 with a sector gear 123a, and a cam 127 installed on the press frame side contacting with the top roller 126 of the oscillating lever 123, said floating die press being a die control device for a powder mold press wherein the ram 101 can descend, corresponding to the variation of predetermined angle on the cam 127. Further, a lower press plate 102 is attached integrally to the lower portion of the upper ram 101, the lower press plate 102 being connected with an upper punch plate 103 of the die set through a joint 104. Moreover, a lower descending press plate 116 is attached integrally to the lower ram 117 thereon, the plate 116 being connected with an injection plate 114 by means of a joint 115.
A plurality of guide rods 106 are vertically embedded in a die plate 107, said rods 106 slidably engaged with the upper punch plate 103 so that an upper punch 105 can enter and leave a die 109.
A die fixing plate 111, secured to a press bolster 112, has a lower punch 110 attached thereto, with the upper portion thereof filled to the die 109 so as to be movable up and down.
Thus, when the upper ram 101 finishes compacting, the lower ram 117 is pulled down by an injection cam (not illustrated) so as to complete injection of a product through descending the die plate 107 to the upper face of the lower punch 110.
The hydraulic cylinder 118 is provided on said lower press plate 102 of the upper ram 101 with a piston 119 having a rod 120 extending downward to the end thereof at which a nut 121 is engaged so as to adjust the length thereof. Corresponding to the descent of the nut 121 by means of said upper punch 105, the clearance between the nut 121 and the rack 122 is lessened, resulting in abutting thereof.
The oscillating lever 123 is pivotally supported by a pin 124 of a bracket 116a disposed on both sides of the lower press plate 116 (the one side not illustrated), on the one side of the oscillating lever 123 being formed a sector gear 123a to engage with the rack 122, whereas at the other end thereof the roller 126 is pivotally supported by a pin 125. A cam 127 is pivotally supported by a pin 128 on the bracket of said press frame wherein the rotation of the cam 127 is restricted by a positioning bolt 129. Returning springs 130a, 130b are attached to the cam 127 and rack 122, respectively.
Further, a support cylinder 133 is connected with the lower press plate 116 so as to keep the lower ram 117 at the predetermined position through a rod 142.
FIG. 2 depicts the commencement of pressing, wherein when 0=o, i.e., the cam 127 is vertical, even though the descending stroke of the upper ram 101 will rotate the sector gear 123a of the oscillating lever 123 by pushing the rack 122 down, the powder 108 is compressed upwards only because the lower press plate 116 of the lower ram 117 is descended only corresponding to the stroke of the upper ram 101, due to the rotation of the cam 127 of the roller 126 of the oscillating lever 123 being restricted by the bolt 129 attached to the press frame. In such a compressing stroke of the lower punch 110, hydraulic oil is poured into the die interior when friction force evolves between the inside wall of the die and the compress powder exceeds the predetermined limit at a relief valve 137 during the hydraulic line, said oil being returnable to a tank 134.
When pressing is commenced with the cam 127 being separated from the roller 126 by setting 0=45.degree. with the cam 127, the lower ram 117 and lower press plate 116 are not both descended, because the descending stroke of the upper ram 101 only rotates the oscillating lever 123. Namely, the die plate 107 is not descended by the action of the hydraulic cylinder 133 but supported by the cylinder 133 of the lower press plate 116. Thus, the powder 108 is only compressed downwards.
When 0=22.5, both the descent of the upper ram 101 and down-pressing of lower ram 117, i.e., the die, become as small as one half, resulting in the die descending at 1/2 speed, relative to that of the upper ram 101. In this case, the cylinder 133 is disposed so as to properly hold the lower ram 117.
The hydraulic circuit of the die-controlling hydraulic cylinder 118 is constructed as follows:
The air is charged from an air source 131 into the upper portion of the air/oil double layer tank 134. The oil fills the die-control cylinder 118, passing through a check valve 136, followed by being pumped by an air-driving hydraulic pump 135 up to the nominated discharge pressure. In this state, the driving air pressure balances with the discharge pressure, causing the end nut 121 of the piston rod 120 which is pushed up to the stroke end of the piston 119, to abut the rack 122 to descend the lower press ram 117.
The hydraulic cylinder 133, a piston and a piston rod 142 are installed on the lower side of the lower press plate 116 of the lower ram 117, at the position symmetrical to the die control hydraulic cylinder 118. Thus, the air source 131 applies pressure to a reducing valve 138 and an air/oil tank 139, making the oil support the weight of the lower ram 117 by lifting the rod 142 upwards from the bottom of the cylinder 133 through a check valve 140. Then, according to the descent of the upper ram 101, the die-control cylinder 118, the piston 119 and the nut 121 make the lower press plate 116 of the lower ram 117 fall down. However, since a relief valve 141 is adjusted to be lower than the hydraulic power of the upper ram 101, the movements of the die plate 107 and die 109 are controlled. Further, as described above, the lower ram 117 is pushed down through adjustment of the cam 127 wherein the lower ram 117 is withdrawn downward with the necessary supporting force being maintained.
The supporting force can be remote-controlled through adjustment of the relief valve 141 regardless of fluctuations in friction between the upper punch 105 and die 109, or between the powder 109 and the inside wall of the die 109, keeping the operation speed and stroke of the die plate 109 constant, depending only on setting of 0, resulting in optional control of the die.
Thus, in the prior art, the combination of the lever 123 with the cam 127 determines the descent timing and rate of speed of the upper punch 105 relative to the die 109 in variations of 1:1 to 1:1/4. In this device, when varying the speed rate, the die control operation timing varies because of variations in abutting position of the cam roller 126 attached to the lever 123 corresponding to the variation in declining angle of the cam 127. Namely, variations in the speed rate can convert the die control timing without conversion of powder feed rate. Further, when also varying the powder feed, the operation timing varies similarly.
However, in this prior art, spaces must be prepared in the press machine proper to receive the lever 123, cam 127 or the like, which is difficult and requires exacting precision in the assembly of these parts. Furthermore, change in the die feeding will vary the operation timing of the die control, and changes in speed rate will vary the timing regardless of changes in the die feeding, except in case of 1:1, which requires readjustment due to unnecessary changes in adjustment.
The present invention provides a die control speed rate conversion device for a powder mold press by overcoming the defects as aforementioned in the prior art.